[dev.typeparams] cmd/compile/internal/importer, types2: initial check-in of types2 and importer

This is a copy of the importer and types2 (unreviewed) prototype version
excluding the testdata directory containing tests (see below). Each file
is marked with the comment

// UNREVIEWED

on the first line. The plan is to check in this code wholesale (it runs and
passes all tests) and then review the code file-by-file via subsequent CLs
and remove the "// UNREVIEWED" comments as we review the files.

Since most tests are unchanged from the original go/types, the next CL will
commit those tests as they don't need to be reviewed again. (Eventually we
may want to factor them out and share them from a single place, e.g. the
test directory.)

The existing file fmtmap_test.go was updated.

Change-Id: I9bd0ad1a7e7188b501423483a44d18e623c0fe71
Reviewed-on: https://go-review.googlesource.com/c/go/+/263624
Trust: Robert Griesemer <gri@golang.org>
Trust: Keith Randall <khr@golang.org>
Run-TryBot: Robert Griesemer <gri@golang.org>
Run-TryBot: Keith Randall <khr@golang.org>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Keith Randall <khr@golang.org>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>

1 files changed, 554 insertions, 0 deletions

diff --git a/src/cmd/compile/internal/types2/subst.go b/src/cmd/compile/internal/types2/subst.go
new file mode 100644
index 0000000000..27c907de10
--- /dev/null
+++ b/src/cmd/compile/internal/types2/subst.go
@@ -0,0 +1,554 @@
+// UNREVIEWED
+// Copyright 2018 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// This file implements instantiation of generic types
+// through substitution of type parameters by actual
+// types.
+
+package types2
+
+import (
+	"bytes"
+	"cmd/compile/internal/syntax"
+	"fmt"
+)
+
+type substMap struct {
+	// The targs field is currently needed for *Named type substitution.
+	// TODO(gri) rewrite that code, get rid of this field, and make this
+	//           struct just the map (proj)
+	targs []Type
+	proj  map[*TypeParam]Type
+}
+
+// makeSubstMap creates a new substitution map mapping tpars[i] to targs[i].
+// If targs[i] is nil, tpars[i] is not substituted.
+func makeSubstMap(tpars []*TypeName, targs []Type) *substMap {
+	assert(len(tpars) == len(targs))
+	proj := make(map[*TypeParam]Type, len(tpars))
+	for i, tpar := range tpars {
+		// We must expand type arguments otherwise *Instance
+		// types end up as components in composite types.
+		// TODO(gri) explain why this causes problems, if it does
+		targ := expand(targs[i]) // possibly nil
+		targs[i] = targ
+		proj[tpar.typ.(*TypeParam)] = targ
+	}
+	return &substMap{targs, proj}
+}
+
+func (m *substMap) String() string {
+	return fmt.Sprintf("%s", m.proj)
+}
+
+func (m *substMap) empty() bool {
+	return len(m.proj) == 0
+}
+
+func (m *substMap) lookup(tpar *TypeParam) Type {
+	if t := m.proj[tpar]; t != nil {
+		return t
+	}
+	return tpar
+}
+
+func (check *Checker) instantiate(pos syntax.Pos, typ Type, targs []Type, poslist []syntax.Pos) (res Type) {
+	if check.conf.Trace {
+		check.trace(pos, "-- instantiating %s with %s", typ, typeListString(targs))
+		check.indent++
+		defer func() {
+			check.indent--
+			var under Type
+			if res != nil {
+				// Calling Under() here may lead to endless instantiations.
+				// Test case: type T[P any] T[P]
+				// TODO(gri) investigate if that's a bug or to be expected.
+				under = res.Underlying()
+			}
+			check.trace(pos, "=> %s (under = %s)", res, under)
+		}()
+	}
+
+	assert(poslist == nil || len(poslist) <= len(targs))
+
+	// TODO(gri) What is better here: work with TypeParams, or work with TypeNames?
+	var tparams []*TypeName
+	switch t := typ.(type) {
+	case *Named:
+		tparams = t.tparams
+	case *Signature:
+		tparams = t.tparams
+		defer func() {
+			// If we had an unexpected failure somewhere don't
+			// panic below when asserting res.(*Signature).
+			if res == nil {
+				return
+			}
+			// If the signature doesn't use its type parameters, subst
+			// will not make a copy. In that case, make a copy now (so
+			// we can set tparams to nil w/o causing side-effects).
+			if t == res {
+				copy := *t
+				res = &copy
+			}
+			// After instantiating a generic signature, it is not generic
+			// anymore; we need to set tparams to nil.
+			res.(*Signature).tparams = nil
+		}()
+
+	default:
+		check.dump("%v: cannot instantiate %v", pos, typ)
+		unreachable() // only defined types and (defined) functions can be generic
+
+	}
+
+	// the number of supplied types must match the number of type parameters
+	if len(targs) != len(tparams) {
+		// TODO(gri) provide better error message
+		check.errorf(pos, "got %d arguments but %d type parameters", len(targs), len(tparams))
+		return Typ[Invalid]
+	}
+
+	if len(tparams) == 0 {
+		return typ // nothing to do (minor optimization)
+	}
+
+	smap := makeSubstMap(tparams, targs)
+
+	// check bounds
+	for i, tname := range tparams {
+		tpar := tname.typ.(*TypeParam)
+		iface := tpar.Bound()
+		if iface.Empty() {
+			continue // no type bound
+		}
+
+		targ := targs[i]
+
+		// best position for error reporting
+		pos := pos
+		if i < len(poslist) {
+			pos = poslist[i]
+		}
+
+		// The type parameter bound is parameterized with the same type parameters
+		// as the instantiated type; before we can use it for bounds checking we
+		// need to instantiate it with the type arguments with which we instantiate
+		// the parameterized type.
+		iface = check.subst(pos, iface, smap).(*Interface)
+
+		// targ must implement iface (methods)
+		// - check only if we have methods
+		check.completeInterface(nopos, iface)
+		if len(iface.allMethods) > 0 {
+			// If the type argument is a type parameter itself, its pointer designation
+			// must match the pointer designation of the callee's type parameter.
+			// If the type argument is a pointer to a type parameter, the type argument's
+			// method set is empty.
+			// TODO(gri) is this what we want? (spec question)
+			if tparg := targ.TypeParam(); tparg != nil {
+				if tparg.ptr != tpar.ptr {
+					check.errorf(pos, "pointer designation mismatch")
+					break
+				}
+			} else if base, isPtr := deref(targ); isPtr && base.TypeParam() != nil {
+				check.errorf(pos, "%s has no methods", targ)
+				break
+			}
+			// If a type parameter is marked as a pointer type, the type bound applies
+			// to a pointer of the type argument.
+			actual := targ
+			if tpar.ptr {
+				actual = NewPointer(targ)
+			}
+			if m, wrong := check.missingMethod(actual, iface, true); m != nil {
+				// TODO(gri) needs to print updated name to avoid major confusion in error message!
+				//           (print warning for now)
+				// check.softErrorf(pos, "%s does not satisfy %s (warning: name not updated) = %s (missing method %s)", targ, tpar.bound, iface, m)
+				if m.name == "==" {
+					// We don't want to report "missing method ==".
+					check.softErrorf(pos, "%s does not satisfy comparable", targ)
+				} else if wrong != nil {
+					// TODO(gri) This can still report uninstantiated types which makes the error message
+					//           more difficult to read then necessary.
+					check.softErrorf(pos,
+						"%s does not satisfy %s: wrong method signature\n\tgot  %s\n\twant %s",
+						targ, tpar.bound, wrong, m,
+					)
+				} else {
+					check.softErrorf(pos, "%s does not satisfy %s (missing method %s)", targ, tpar.bound, m.name)
+				}
+				break
+			}
+		}
+
+		// targ's underlying type must also be one of the interface types listed, if any
+		if iface.allTypes == nil {
+			continue // nothing to do
+		}
+		// iface.allTypes != nil
+
+		// If targ is itself a type parameter, each of its possible types, but at least one, must be in the
+		// list of iface types (i.e., the targ type list must be a non-empty subset of the iface types).
+		if targ := targ.TypeParam(); targ != nil {
+			targBound := targ.Bound()
+			if targBound.allTypes == nil {
+				check.softErrorf(pos, "%s does not satisfy %s (%s has no type constraints)", targ, tpar.bound, targ)
+				break
+			}
+			for _, t := range unpack(targBound.allTypes) {
+				if !iface.isSatisfiedBy(t.Under()) {
+					// TODO(gri) match this error message with the one below (or vice versa)
+					check.softErrorf(pos, "%s does not satisfy %s (%s type constraint %s not found in %s)", targ, tpar.bound, targ, t, iface.allTypes)
+					break
+				}
+			}
+			break
+		}
+
+		// Otherwise, targ's type or underlying type must also be one of the interface types listed, if any.
+		if !iface.isSatisfiedBy(targ) {
+			check.softErrorf(pos, "%s does not satisfy %s (%s not found in %s)", targ, tpar.bound, targ.Under(), iface.allTypes)
+			break
+		}
+	}
+
+	return check.subst(pos, typ, smap)
+}
+
+// subst returns the type typ with its type parameters tpars replaced by
+// the corresponding type arguments targs, recursively.
+// subst is functional in the sense that it doesn't modify the incoming
+// type. If a substitution took place, the result type is different from
+// from the incoming type.
+func (check *Checker) subst(pos syntax.Pos, typ Type, smap *substMap) Type {
+	if smap.empty() {
+		return typ
+	}
+
+	// common cases
+	switch t := typ.(type) {
+	case *Basic:
+		return typ // nothing to do
+	case *TypeParam:
+		return smap.lookup(t)
+	}
+
+	// general case
+	subst := subster{check, pos, make(map[Type]Type), smap}
+	return subst.typ(typ)
+}
+
+type subster struct {
+	check *Checker
+	pos   syntax.Pos
+	cache map[Type]Type
+	smap  *substMap
+}
+
+func (subst *subster) typ(typ Type) Type {
+	switch t := typ.(type) {
+	case nil:
+		// Call typOrNil if it's possible that typ is nil.
+		panic("nil typ")
+
+	case *Basic, *bottom, *top:
+		// nothing to do
+
+	case *Array:
+		elem := subst.typOrNil(t.elem)
+		if elem != t.elem {
+			return &Array{len: t.len, elem: elem}
+		}
+
+	case *Slice:
+		elem := subst.typOrNil(t.elem)
+		if elem != t.elem {
+			return &Slice{elem: elem}
+		}
+
+	case *Struct:
+		if fields, copied := subst.varList(t.fields); copied {
+			return &Struct{fields: fields, tags: t.tags}
+		}
+
+	case *Pointer:
+		base := subst.typ(t.base)
+		if base != t.base {
+			return &Pointer{base: base}
+		}
+
+	case *Tuple:
+		return subst.tuple(t)
+
+	case *Signature:
+		// TODO(gri) rethink the recv situation with respect to methods on parameterized types
+		// recv := subst.var_(t.recv) // TODO(gri) this causes a stack overflow - explain
+		recv := t.recv
+		params := subst.tuple(t.params)
+		results := subst.tuple(t.results)
+		if recv != t.recv || params != t.params || results != t.results {
+			return &Signature{
+				rparams:  t.rparams,
+				tparams:  t.tparams,
+				scope:    t.scope,
+				recv:     recv,
+				params:   params,
+				results:  results,
+				variadic: t.variadic,
+			}
+		}
+
+	case *Sum:
+		types, copied := subst.typeList(t.types)
+		if copied {
+			// Don't do it manually, with a Sum literal: the new
+			// types list may not be unique and NewSum may remove
+			// duplicates.
+			return NewSum(types)
+		}
+
+	case *Interface:
+		methods, mcopied := subst.funcList(t.methods)
+		types := t.types
+		if t.types != nil {
+			types = subst.typ(t.types)
+		}
+		embeddeds, ecopied := subst.typeList(t.embeddeds)
+		if mcopied || types != t.types || ecopied {
+			iface := &Interface{methods: methods, types: types, embeddeds: embeddeds}
+			subst.check.posMap[iface] = subst.check.posMap[t] // satisfy completeInterface requirement
+			subst.check.completeInterface(nopos, iface)
+			return iface
+		}
+
+	case *Map:
+		key := subst.typ(t.key)
+		elem := subst.typ(t.elem)
+		if key != t.key || elem != t.elem {
+			return &Map{key: key, elem: elem}
+		}
+
+	case *Chan:
+		elem := subst.typ(t.elem)
+		if elem != t.elem {
+			return &Chan{dir: t.dir, elem: elem}
+		}
+
+	case *Named:
+		subst.check.indent++
+		defer func() {
+			subst.check.indent--
+		}()
+		dump := func(format string, args ...interface{}) {
+			if subst.check.conf.Trace {
+				subst.check.trace(subst.pos, format, args...)
+			}
+		}
+
+		if t.tparams == nil {
+			dump(">>> %s is not parameterized", t)
+			return t // type is not parameterized
+		}
+
+		var new_targs []Type
+
+		if len(t.targs) > 0 {
+
+			// already instantiated
+			dump(">>> %s already instantiated", t)
+			assert(len(t.targs) == len(t.tparams))
+			// For each (existing) type argument targ, determine if it needs
+			// to be substituted; i.e., if it is or contains a type parameter
+			// that has a type argument for it.
+			for i, targ := range t.targs {
+				dump(">>> %d targ = %s", i, targ)
+				new_targ := subst.typ(targ)
+				if new_targ != targ {
+					dump(">>> substituted %d targ %s => %s", i, targ, new_targ)
+					if new_targs == nil {
+						new_targs = make([]Type, len(t.tparams))
+						copy(new_targs, t.targs)
+					}
+					new_targs[i] = new_targ
+				}
+			}
+
+			if new_targs == nil {
+				dump(">>> nothing to substitute in %s", t)
+				return t // nothing to substitute
+			}
+
+		} else {
+
+			// not yet instantiated
+			dump(">>> first instantiation of %s", t)
+			new_targs = subst.smap.targs
+
+		}
+
+		// before creating a new named type, check if we have this one already
+		h := instantiatedHash(t, new_targs)
+		dump(">>> new type hash: %s", h)
+		if named, found := subst.check.typMap[h]; found {
+			dump(">>> found %s", named)
+			subst.cache[t] = named
+			return named
+		}
+
+		// create a new named type and populate caches to avoid endless recursion
+		tname := NewTypeName(subst.pos, t.obj.pkg, t.obj.name, nil)
+		named := subst.check.NewNamed(tname, t.underlying, t.methods) // method signatures are updated lazily
+		named.tparams = t.tparams                                     // new type is still parameterized
+		named.targs = new_targs
+		subst.check.typMap[h] = named
+		subst.cache[t] = named
+
+		// do the substitution
+		dump(">>> subst %s with %s (new: %s)", t.underlying, subst.smap, new_targs)
+		named.underlying = subst.typOrNil(t.underlying)
+		named.orig = named.underlying // for cycle detection (Checker.validType)
+
+		return named
+
+	case *TypeParam:
+		return subst.smap.lookup(t)
+
+	case *instance:
+		// TODO(gri) can we avoid the expansion here and just substitute the type parameters?
+		return subst.typ(t.expand())
+
+	default:
+		unimplemented()
+	}
+
+	return typ
+}
+
+// TODO(gri) Eventually, this should be more sophisticated.
+//           It won't work correctly for locally declared types.
+func instantiatedHash(typ *Named, targs []Type) string {
+	var buf bytes.Buffer
+	writeTypeName(&buf, typ.obj, nil)
+	buf.WriteByte('(')
+	writeTypeList(&buf, targs, nil, nil)
+	buf.WriteByte(')')
+
+	// With respect to the represented type, whether a
+	// type is fully expanded or stored as instance
+	// does not matter - they are the same types.
+	// Remove the instanceMarkers printed for instances.
+	res := buf.Bytes()
+	i := 0
+	for _, b := range res {
+		if b != instanceMarker {
+			res[i] = b
+			i++
+		}
+	}
+
+	return string(res[:i])
+}
+
+func typeListString(list []Type) string {
+	var buf bytes.Buffer
+	writeTypeList(&buf, list, nil, nil)
+	return buf.String()
+}
+
+// typOrNil is like typ but if the argument is nil it is replaced with Typ[Invalid].
+// A nil type may appear in pathological cases such as type T[P any] []func(_ T([]_))
+// where an array/slice element is accessed before it is set up.
+func (subst *subster) typOrNil(typ Type) Type {
+	if typ == nil {
+		return Typ[Invalid]
+	}
+	return subst.typ(typ)
+}
+
+func (subst *subster) var_(v *Var) *Var {
+	if v != nil {
+		if typ := subst.typ(v.typ); typ != v.typ {
+			copy := *v
+			copy.typ = typ
+			return &copy
+		}
+	}
+	return v
+}
+
+func (subst *subster) tuple(t *Tuple) *Tuple {
+	if t != nil {
+		if vars, copied := subst.varList(t.vars); copied {
+			return &Tuple{vars: vars}
+		}
+	}
+	return t
+}
+
+func (subst *subster) varList(in []*Var) (out []*Var, copied bool) {
+	out = in
+	for i, v := range in {
+		if w := subst.var_(v); w != v {
+			if !copied {
+				// first variable that got substituted => allocate new out slice
+				// and copy all variables
+				new := make([]*Var, len(in))
+				copy(new, out)
+				out = new
+				copied = true
+			}
+			out[i] = w
+		}
+	}
+	return
+}
+
+func (subst *subster) func_(f *Func) *Func {
+	if f != nil {
+		if typ := subst.typ(f.typ); typ != f.typ {
+			copy := *f
+			copy.typ = typ
+			return &copy
+		}
+	}
+	return f
+}
+
+func (subst *subster) funcList(in []*Func) (out []*Func, copied bool) {
+	out = in
+	for i, f := range in {
+		if g := subst.func_(f); g != f {
+			if !copied {
+				// first function that got substituted => allocate new out slice
+				// and copy all functions
+				new := make([]*Func, len(in))
+				copy(new, out)
+				out = new
+				copied = true
+			}
+			out[i] = g
+		}
+	}
+	return
+}
+
+func (subst *subster) typeList(in []Type) (out []Type, copied bool) {
+	out = in
+	for i, t := range in {
+		if u := subst.typ(t); u != t {
+			if !copied {
+				// first function that got substituted => allocate new out slice
+				// and copy all functions
+				new := make([]Type, len(in))
+				copy(new, out)
+				out = new
+				copied = true
+			}
+			out[i] = u
+		}
+	}
+	return
+}